MAN AS A MAKER OF NEW PLANTS — ANDERSON 463 



spread, and did pioneers or primitive man have anything to do with 

 making this previous niche ? This is the sort of question we are now 

 making the subject of decisive experiments ; we do not yet have enough 

 results for decisive answers. 



For micro-organisms the problem of the species that travel about 

 with man staggers the imagination. Micro-organisms seemingly fall 

 into the same general categories as macro-organisms. Brewers' yeasts 

 are as much cultivated plants as the barleys and wheats with which 

 they have so long been associated for brewing and baking. The germs 

 of typhoid and cholera are quite as much weeds as are dandelions or 

 Canada thistles. The micro-organisms of our garden soil are appar- 

 ently the same mixture of mongrel immigrants and adapted natives 

 as our meadow and pasture plants. Soils are good or bad quite as 

 much because of the microcommunities they contain as because of 

 their composition. Man's unconscious creation of new kinds of micro- 

 organisms is an important part of his total effect on the landscapes 

 of the world. Think, then, of this total composite mantle of living 

 things which accompanies man : the crops, the weeds, the domesticated 

 animals, the garden escapes such as Japanese honeysuckle and orange 

 day lily, the thorn scrub, the bamboo thickets, the English sparrows, 

 the starlings, the insect pests. Think of the great clouds of algae, 

 protozoa, bacteria, and fungi — complex communities of micro-organ- 

 isms that inhabit our soils, our beverages, our crops, our domesticated 

 animals, and our very bodies. 



If we turn to the scientific literature for an orderly summary of 

 where these species came from and how, there is a depressing lack of 

 information. The crop plants and domesticated animals have been 

 somewhat studied, the ornamentals and the weeds scarcely investi- 

 gated. Even for the crop plants one notes that for those that have 

 been the most carefully studied — wheat (Aase, 1946), cotton (Hutch- 

 inson et al., 1947), maize (Mangelsdorf and Reeves, 1938) — there is 

 now general recognition that their origins, relationships, and exact 

 histories are much more complex problems than they were thought to 

 be a generation ago. In spite of these wide gaps in our knowledge, 

 I believe the following generalizations will stand : 



1. All the major crops and most of the minor ones were domesti- 

 cated in prehistoric times. Modern agriculture, classified solely by 

 the plants it uses, is Neolithic agriculture. 



2. For none of the major crops can we point with certainty to the 

 exact species (or combination of species) from which it was derived: 

 for some we can make guesses ; for a number we can point to closely 

 related weeds. This merely complicates the problem. We then have 

 to determine the origin of the crop, the origin of the weed, and the 

 history of their relationships. 



